266 Heredity. 



easier to appreciate its influence on the mind of the patient ; when 

 it ceases, he is docile and affectionate. When it reappears, his 

 evil instincts return, and we have had reason to know that they 

 might have led him even to murder.' 



It has been observed that when there is perfect physical similarity 

 between twins, which is not rare, it is always accompanied with 

 moral similarity. Moreau saw at Bicetre two young men who were 

 so much alike that one would be taken for the other. They both 

 possess the same monomania, the same dominant ideas, the same 

 hallucinations of hearing ; they never speak to any one, nor do 

 they communicate with one another. 'An exceedingly curious fact, 

 often observed by the attendants and by myself, is this : from time 

 to time, at irregular intervals of two, three, or more months, 

 without appreciable cause, and by the entirely spontaneous action 

 of their malady, a very marked change occurs in both brothers at 

 the same period ; often on the same day they quit their habitual 

 state of stupor and prostration and earnestly entreat the physician 

 to give them their freedom. I have seen this repeated even when 

 the two brothers were separated from one another by a distance 

 of several miles.' l 



The phenomenon of suggestion also, as produced in magnetized 

 subjects, and in the state of catalepsy or hypnotism, supplies 

 decisive facts in support of our proposition. Ordinarily, the ideas, 

 sentiments, and volitions suggest the sign, and are interpreted by 

 it; here, on the contrary, the sign suggests the idea, the sentiment, 

 the volition. The phenomenon is reversed. Thus, by placing 

 the magnetized person on his knees, the thoughts of humility and 

 reverence are suggested; by lifting up his lips and his eyelids in a 

 certain way, he is rendered proud and haughty; by raising his arms 

 into the air, or clasping his hands on some object, he is made to 

 think that he is climbing. Carpenter has collected a number of 

 facts of this kind. 



It may therefore be said that experience supplies decisive facts 

 to confirm our proposition, that every psychological phenomenon 

 has a physiological antecedent. It cannot be asserted on sound 

 logical grounds that this is certain. To make it so, the proposition 



1 Op. cit., p. 172. See an analogous fact in Trousseau, Clinique Mldicale, 

 253- 



